Compound and coating compositions for adhesion to olefinic substrates

ABSTRACT

The present invention provides an olefin-based block copolymer that has an olefin block that is substantially saturated and at least one (poly)ester or (poly)ether block. The olefin-based block copolymer of the invention can be prepared by reacting a liquid hydroxyl-functional, saturated or substantially saturated olefin polymer with a chain-extension reagent that is reactive with hydroxyl groups and will polymerize in a head-to-tail arrangement of monomer units. The olefin-based block copolymer of the invention can be used to prepare an adhesion promoter that provides excellent adhesion of subsequent coating layers to olefinic substrates like TPO and superior properties as compared to previously used adhesion promoters containing chlorinated polyolefins. Alternatively, the olefin-based copolymers of the invention can be used as an additive in a curable coating composition to provide excellent adhesion to olefinic substrates like TPO, even when used in very minor amounts compared to the amounts required for previously known agents.

FIELD OF THE INVENTION

[0001] This invention concerns curable coating compositions, especiallycompositions that are applied over olefinic substrates, particularlythermoplastic polyolefin (TPO) substrates.

BACKGROUND OF THE INVENTION

[0002] It is often desirable, for decorative or functional reasons, toapply a coating over a plastic substrate. For certain substrates it hasbeen difficult to find coating compositions that provide the requiredadhesion at a reasonable price and with suitable physical properties. Itis well-known that it is difficult to obtain good adhesion of paints toolefinic substrates, including thermoplastic polyolefin (TPO) substratesand other such modified polyolefin-based materials.

[0003] In addition to painted articles, TPO has been used in acolor-in-mold process to produce articles of the desired colored thatare not intended to be painted, so long as the requirements forappearance are not stringent. The color-in-mold process, however, is notadequate for producing high class (“class 1”) surfaces for a number ofreasons. First, it is difficult to achieve high gloss finishes, anddifficult to control the gloss of the finish reproducibly from onearticle to the next. Secondly, TPO is relatively soft and it woulddesirable to coat the substrate with a coating composition that canoffer resistance to marring and scratching. Finally, uncoated orunpainted TPO may have unsatisfactory weathering properties (i.e., maydegrade, discolor, or chalk during outdoor exposure) in certainapplications, whereas it is known that coatings provide good weatheringcharacteristics to many different substrates. For these reasons, then,it would be desirable to have a means of applying a coating compositionto an olefinic substrate to provide the properties lacking in theuncoated (raw) uncolored or colored substrate.

[0004] Plastic substrates may be coated with curable, or thermosettable,coating compositions. Thermosettable coating compositions are widelyused in the coatings art, particularly for high-performance primers andtopcoats. Color-plus-clear composite coatings have been particularlyuseful as topcoats for which exceptional gloss, depth of color,distinctness of image, or special metallic effects are desired.

[0005] In the past, it has been necessary to include one or moreadditional separate manufacturing steps to prepare an olefinic substratefor painting so that the coating layer will be able to adhere to theolefinic substrate. According to one frequently used method, a thinlayer of an adhesion promoter or tie layer is applied directly to theolefinic substrate. The desired coating layer or layers are then appliedover the adhesion promoter. Such adhesion promoters typically include achlorinated polyolefin. Adhesion promoters with chlorinated polyolefinsare expensive to use, often exhibit instability, and, if used in a clear(unpigmented) composition, produce colored, hazy films. In addition, thechlorinated polyolefin materials may produce coatings with poor exteriordurability because they are susceptible to degradation when exposed toUV light. Another method that has been used to prepare an olefinicsubstrate to receive a coating layer is chemical modification of thesubstrate surface, for example by flame or corona pretreatment.

[0006] Recently, coating compositions that include significantconcentrations of adhesion promoting agents in order to achieve goodadhesion to olefinic substrates have been proposed. Publishedinternational application WO 97/35937 describes a composition thatincludes 5-45% by weight of resin solids of a substantially saturatedpolyhdroxylated polydiene polymer having terminal hydroxyl groups.International Publication Number WO 97/35937 and all of the referencescited therein are hereby incorporated herein by reference. Theinternational publication '937 discloses that such polymers are thehydrogenated product of dihydroxy polybutadiene produced by anionicpolymerization of conjugated diene hydrocarbon capped with two moles ofethylene oxide and terminated with two moles of methanol. (The ethyleneoxide produces the oxygenated anion, and the methanol provides thehydrogen cation to form the hydroxyl group.) The large amount of thisadhesion promoting agent that must be included may adversely affectphysical properties and appearance of the resulting coating. Inaddition, compositions that include significant concentrations of theadhesion promoting agent may separate into phases because the differentcomponents frequently are not very compatible. The '937 referencerequires a specific solvent package that may be undesirable in manyinstances. The same problems are encountered with other prior artadhesion promoting agents such as chlorinated polyolefins. It is alsoknown that including chlorinated polyolefins in some coatingcompositions, e.g., curable coating compositions that include acidcatalysts, can result in adverse interactions between the differentcomponents of the coating composition.

[0007] It is an object of the present invention to provide a materialthat can be used to prepare an adhesion promoter or used as an adhesionpromoting agent or additive in a coating composition to provideexcellent adhesion to uncoated olefinic substrates while overcoming thedrawbacks of the compositions and methods previously used.

SUMMARY OF THE INVENTION

[0008] The present invention provides an olefin-based block copolymerthat has an olefin block and at least one (poly)ester or (poly)etherblock. By the terms “(poly)ester block” and “(poly)ether block” it ismeant that the base polyolefin material is modified with one or more onemonomer units through formation of, respectively, ester or etherlinkages. For purposed of the present invention, “(poly)ester block” hasa special meaning that, in the case of two or more monomer units, themonomer units are predominantly, preferably exclusively, arranged inhead-to-tail linkages. Thus, the arrangement of the ester linkages inthe (poly)ester block or blocks may be represented by

[0009] in which n represents the number of monomer units, R representsthe part of each monomer unit between the ester groups (which may be allthe same if only one type of monomer is used or different for individualunits if a mixture of different monomers is used), and Y represents theendgroup of the block. The monomer units should be arranged exclusivelyin the head-to-tail arrangement, although it is possible, particularlyin longer blocks, for there to be some variation; in the latter case,the arrangement should still be predominantly head-to-tail. Preferredembodiments for n, R, and Y are described below.

[0010] The olefin-based block copolymer of the invention can be preparedby reacting a liquid hydroxyl-functional, saturated or substantiallysaturated olefin polymer with a chain-extension reagent that is reactivewith hydroxyl groups and will polymerize in a head-to-tail arrangementof monomer units. Such chain-extension reagents include, withoutlimitation, lactones, hydroxy carboxylic acids, oxirane-functionalmaterials such as alkylene oxides, and combinations of these. Preferredchain-extension reagents are lactones and alkylene oxides, and even morepreferred are epsilon caprolactone, ethylene oxide, and propylene oxide.

[0011] The olefin-based block copolymer of the invention can be used toprepare an adhesion promoter that provides excellent adhesion ofsubsequent coating layers to olefinic substrates like TPO at a muchlower cost than the previously used adhesion promoters containingchlorinated polyolefins. Alternatively, the olefin-based copolymers ofthe invention can be used as an additive in a curable coatingcomposition to provide excellent adhesion to olefinic substrates likeTPO, even when used in very minor amounts compared to the amountsrequired for previously known agents. The adhesion promoter or coatingcomposition of the invention is applied directly to an unmodifiedplastic substrate, in other words to a plastic substrate that has noflame or corona pretreatment or any other treatment meant to chemicallymodify the surface of the substrate and to which no previous adhesionpromoter or coating has been applied.

[0012] When used as an additive, the olefin-based block copolymer of theinvention may be added to a variety of coating compositions to providegood adhesion to TPO and other olefinic substrates, even at relativelylow levels of the olefin-based block copolymer. Compositions of theinvention include primers, one-layer topcoats, basecoats, andclearcoats. In one preferred method according to the invention, aclearcoat composition containing the olefin-based block copolymer isapplied over a colored TPO substrate.

[0013] Coating compositions according to the invention that include theblock copolymer additive can be formulated to provide gloss over a widerange of values suited to particular applications. In addition, thecompositions of the invention can impart desirable surface properties tothe TPO or olefinic articles, such as resistance to scratching andmarring, as well as enhance the weathering durability of such articles.

DETAILED DESCRIPTION

[0014] The olefin-based block copolymer of the invention has at leastone block that is a (poly)ester or (poly)ether block and at least oneblock is an olefin material. Preferably, the block copolymer has oneblock of the olefin material to which is attached one or more of the(poly)ester and/or (poly)ether blocks. In one embodiment, theolefin-based block copolymer of the invention can be represented by astructure

A−[O−(B)]_(m),

[0015] in which A represents an olefin block, B represents a (poly)esteror (poly)ether block or combinations thereof, and m is on average fromabout 0.7 to about 10, preferably from about 1.7 to about 2.2, andparticularly preferably about 1.9 or 2. The A block is a saturated orsubstantially saturated olefin polymer. The B block preferably contains,on average, from about 0.5 to about 25 monomer units, more preferablythe B block has on average from about 2 to about 10, and even morepreferably from about 2 to about 6, monomer units per hydroxyl group ofthe unmodified olefin block. The monomer units may be the same or theremay be different monomer units in a single (poly)ester or (poly)etherblock. For example, a (poly)ether block may have one or more ethyleneoxide units and one or more propylene oxide units.

[0016] The olefin-based block copolymer of the invention can be preparedby reacting a hydroxyl-functional olefin polymer with a chain-extensionreagent that is reactive with hydroxyl groups and will polymerize in ahead-to-tail arrangement of monomer units. The hydroxyl-functionalolefin forms the A block, which the chain-extension reagent forms the Bblock or blocks. Such chain-extension reagents include, withoutlimitation, lactones, hydroxy carboxylic acids, oxirane-functionalmaterials such as alkylene oxides, and combinations of these. Preferredchain-extension reagents are lactones and alkylene oxides, and even morepreferred are epsilon caprolactone, ethylene oxide, propylene oxide, andcombinations of these.

[0017] The hydroxyl-functional olefin polymer may be produced byhydrogenation of a polyhydroxylated polydiene polymer. Polyhydroxylatedpolydiene polymers may produced by anionic polymerization of monomerssuch as isoprene or butadiene and capping the polymerization productwith alkylene oxide and methanol, as described in U.S. Pat. Nos.5,486,570, 5,376,745, 4,039,593, and Reissue 27,145, each of which isincorporated herein by reference. The polyhydroxylated polydiene polymeris substantially saturated by hydrogenation of the double bonds that isat least 90 percent, preferably at least 95% and even more preferablyessentially 100% complete to form the hydroxyl-functional olefinpolymer. The hydroxyl equivalent weight of the hydroxyl-functionalsaturated olefin polymer may be from about 500 to about 20,000.

[0018] The hydroxyl-functional olefin polymer is preferably ahydroxyl-functional ethylene/butylene polymer. Preferred olefin polymersmay have a number average molecular weight of from about 2000 to about10,000. Preferably, the olefin polymer is a liquidpoly(ethylene/butylene) polymer having at least one hydroxyl group.Preferably, the olefin polymer has from about 0.7 to about 10 hydroxylgroups on average per molecule, more preferably from about 1.7 to about2.2 hydroxyl groups on average per molecule, and still more preferablyabout 2 hydroxyl groups on average per molecule. The hydroxyl-functionalolefin polymer preferably has terminal hydroxyl groups and a hydroxylequivalent weight of from about 1000 to about 3000.

[0019] Such materials are commercially available from Shell ChemicalCompany, Houston, TX, under the tradename KRATON LIQUID. One preferredmaterial is KRATON LIQUID L-2203, an anionically polymerized, polymericdiol containing terminal primary hydroxyl groups, that is available fromShell Chemicals. Anionic polymerization results in polymers having avery narrow molecular weight distribution. Molecular weightdistributions of less than about 1.2, particularly about 1.1 or less,are preferred for these materials.

[0020] While not wishing to be bound by theory, it is believed that themechanism that results in adhesion of the coating to the substrateinvolves a migration of the olefin-based block copolymer to the olefinicor TPO substrate interface and an interaction with the olefinic or TPOsubstrate. It is believed that the migration and/or interaction isfacilitated by application of heat, such as the heat applied to cure thecoating composition. It is also believed that the migration and/orinteraction is facilitated by predominantly lower molecular weightmolecules. Olefin-based block copolymers having narrower polydispersity(i.e., closer to the ideal of 1), in which high molecular weightfractions are less than for materials having similar number averagemolecular weights but broader (higher) polydispersity, are believed tooffer an advantage in either better adhesion at lower levels ofincorporation or effective adhesion achieved under milder conditions(lower temperatures and/or shorter interaction times). “Polydispersity,”also known simply as “dispersity,” is defined in polymer science as theratio of the weight average molecular weight to the number averagemolecular weight. Higher polydispersity numbers indicate a broaderdistribution of molecular weights, and in particular mean a largerfraction of higher molecular weight species.

[0021] The olefin-based block copolymer of the invention thus preferablyhas a narrow polydispersity. When the liquid olefin polymer isanionically polymerized it may have a very narrow polydispersity, suchas on the order of only about 1.1. The ring-opening reactions oflactones and alkylene oxides or reactions of other materials that addhead-to-tail like the hydroxy carboxylic acids tend to produce polymersthat are more uniform and have narrow polydispersities. Modification ofthe olefin polymer by a head-to-tail reaction such as a ring-openingreaction of a lactone or alkylene oxide compound usually results in aproduct having a polydispersity of about 1.1 or 1.15, thus essentiallypreserving the narrow polydispersity of the hydroxyl-functional olefinstarting material. Block copolymers of the invention preferably havepolydispersities of about 1.2 or less, and more preferably havepolydispersities of about 1.15 or less.

[0022] Again while not wishing to be bound by theory, it is believedthat the modification of the liquid olefin polymer by the (poly)ester or(poly)ether block or blocks offers significant advantages in providingadhesion of coatings to olefinic substrates because of increasedcompatibility of the resulting block copolymer toward materials commonlyemployed in such coatings. In addition, the imposition of the(poly)ester or (poly)ether block between the olefin block and thefunctional group, such as the hydroxyl group, makes that functionalgroup more accessible for reaction during the curing of the coatingcomposition. These principles can be used to optimize the olefin-basedblock copolymer of the invention for use under particular conditions orwith or in particular coating compositions.

[0023] In a preferred embodiment, the olefin polymer is reacted with alactone or a hydroxy carboxylic acid to form an olefin-based polymerhaving (poly)ester end blocks. Lactones that can be ring opened by anactive hydrogen are well-known in the art. Examples of suitable lactonesinclude, without limitation, ε-caprolactone, γ-caprolactone,δ-butyrolactone, δ-propriolactone, γ-butyrolactone,α-methyl-γ-butyrolactone, δ-methyl-γ-butyrolactone, γ-valerolactone,δ-valerolactone, γ-decanolactone, δ-decanolactone, γ-nonanoic lactone,γ-octanoic lactone, and combinations of these. In one preferredembodiment, the lactone is ε-caprolactone. Lactones useful in thepractice of the invention can also be characterized by the formula:

[0024] wherein n is a positive integer of 1 to 7 and R is one or more Hatoms, or substituted or unsubstituted alkyl groups of 1-7 carbon atoms.

[0025] The lactone ring-opening reaction is typically conducted underelevated temperature (e.g., 80-150° C.). When the reactants are liquidsa solvent is not necessary. However, a solvent may be useful inpromoting good conditions for the reaction even when the reactants areliquid. Any non-reactive solvent may be used, including both polar andnonpolar organic solvents. Examples of useful solvents include, withoutlimitation, toluene, xylene, methyl ethyl ketone, methyl isobutylketone, and the like and combinations of such solvents. A catalyst ispreferably present. Useful catalysts include, without limitation, protonacids (e.g., octanoic acid, Amberlyst® 15 (Rohm & Haas)), and tincatalysts (e.g., stannous octoate). Alternatively, the reaction can beinitiated by forming a sodium salt of the hydroxyl group on themolecules that will react with the lactone ring.

[0026] A hydroxy carboxylic acid can also be used instead of a lactoneor in combination with a lactone as the compound that reacts with theliquid olefin polymer to provide ester blocks. Useful hydroxy carboxylicacids include, without limitation, dimethylhydroxypropionic acid,hydroxy stearic acid, tartaric acid, lactic acid, 2-hydroxyethyl benzoicacid, N-(2-hydroxyethyl)ethylene diamine triacetic acid, andcombinations of these. The reaction can be conducted under typicalesterification conditions, for example at temperatures from roomtemperature up to about 150° C., and with catalysts such as, forexample, calcium octoate, metal hydroxides like potassium hydroxide,Group I or Group II metals such as sodium or lithium, metal carbonatessuch as potassium carbonate or magnesium carbonate (which may beenhanced by use in combination with crown ethers), organometallic oxidesand esters such as dibutyl tin oxide, stannous octoate, and calciumoctoate, metal alkoxides such as sodium methoxide and aluminumtripropoxide, protic acids like sulfuric acid, or Ph₄SbI. The reactionmay also be conducted at room temperature with a polymer-supportedcatalyst such as Amerlyst-15® (available from Rohm & Haas) as describedby R. Anand in Synthetic Communications, 24(19), 2743-47 (1994), thedisclosure of which is incorporated herein by reference.

[0027] While polyester segments may likewise be produced with dihydroxyand dicarboxylic acid compounds, it is preferred to avoid such compoundsbecause of the tendency of reactions involving these compounds toincrease the polydispersity of the resulting block copolymer. If used,these compounds should be used in limited amounts and preferablyemployed only after the lactone or hydroxy carboxylic acid reactantshave fully reacted.

[0028] The reaction with the lactone or hydroxy carboxylic acid oroxirane compounds adds at least one monomer unit as the B block andpreferably provides chain extension of the olefin polymer. Inparticular, the (poly)ester and/or (poly)ether block is thought toaffect the polarity and effective reactivity of the end groupfunctionality during curing of the coating. The (poly)ester and/or(poly)ether block also makes the olefin-based block copolymer morecompatible with components of a typical curable coating composition. Theamount of the extension depends upon the moles of the alkylene oxide,lactone, and/or hydroxy carboxylic acid available for reaction. Therelative amounts of the olefin polymer and the alkylene oxide, lactone,and/or hydroxy acid can be varied to control the degree of chainextension. The reaction of the lactone ring, oxirane ring, and/orhydroxy carboxylic acid with a hydroxyl group results in the formationof an ether or ester and a new resulting hydroxyl group that can thenreact with another available monomer, thus providing the desired chainextension. In the preferred embodiments of the present invention, theequivalents of oxirane, lactone, and/or hydroxy carboxylic acid for eachequivalent of hydroxyl on the olefin polymer are from about 0.5 to about25, more preferably from about 1 to about 10, and even more preferablyfrom about 2 to about 6. In an especially preferred embodiment about 2.5equivalents of lactone are reacted for each equivalent of hydroxyl onthe olefin polymer.

[0029] In another embodiment of the invention, a polyolefin havingterminal hydroxyl groups is reacted with an oxirane-containing compoundto produce (poly)ether endblocks. The oxirane-containing compound ispreferably an alkylene oxide or cyclic ether, especially preferably acompound selected from ethylene oxide, propylene oxide, butylene oxide,tetrahydrofuran, and combinations of these. Alkylene oxide polymersegments include, without limitation, the polymerization products ofethylene oxide, propylene oxide, 1,2-cyclohexene oxide, 1-butene oxide,2-butene oxide, 1-hexene oxide, tert-butylethylene oxide, phenylglycidyl ether, 1-decene oxide, isobutylene oxide, cyclopentene oxide,1-pentene oxide, and combinations of these. The hydroxyl group of theolefin-based polymer functions as initiator for the base-catalyzedalkylene oxide polymerization. The polymerization may be carried out,for example, by charging the hydroxyl-terminated olefin polymer and acatalytic amount of caustic, such as potassium hydroxide, sodiummethoxide, or potassium tert-butoxide, and adding the alkylene oxide ata sufficient rate to keep the monomer available for reaction. Two ormore different alkylene oxide monomers may be randomly copolymerized bycoincidental addition and polymerized in blocks by sequential addition.

[0030] Tetrahydrofuran polymerizes under known conditions to formrepeating units

—[CH₂CH₂CH₂CH₂O]—

[0031] Tetrahydrofuran is polymerized by a cationic ring-openingreaction using such counterions as SbF₆ ^(—), AsF₆ ^(—), PF₆ ^(—), SbCl₆^(—), BF₄ ^(—), CF₃SO₃ ^(—), FSO₃ ^(—), and ClO₄ ^(—). Initiation is byformation of a tertiary oxonium ion. The polytetrahydrofuran segment canbe prepared as a “living polymer” and terminated by reaction with thehydroxyl group of the olefin polymer.

[0032] It is also highly desirable for the olefin-based block copolymerof the invention to have functional groups that are reactive with one ormore film-forming components of the adhesion promoter, or of the coatingcomposition applied over an adhesion promoter containing theolefin-based block copolymer, or of the coating composition to which theolefin-based block copolymer is added. The film-forming components withwhich the olefin-based block copolymer may be reactive may be afilm-forming polymer or a curing agent. The reactive functional groupson the olefin-based block copolymer may include, without limitation,hydroxyl, carbamate, urea, carboxylic acid, and combinations of these.Following addition of the ether or ester blocks, the block copolymer ofthe invention has one or more hydroxyl groups, which may be reactivewith the film-forming polymer or curing agent. If desired, the hydroxylgroups may be converted to other functional groups, including carbamate,urea, carboxylic acid groups and combinations of these. Carbamate groupsaccording to the invention can be represented by the structure

[0033] in which R is H or alkyl, preferably of 1 to 4 carbon atoms.Preferably R is H or methyl, and more preferably R is H. Urea groupsaccording to the invention can be represented by the structure

[0034] in which R′ and R″ are each independently H or alkyl, or R′ andR″ together form a heterocyclic ring structure. Preferably, R′ and R″are each independently H or alkyl of from 1 to about 4 carbon atoms ortogether form an ethylene bridge, and more preferably R′ and R″ are eachindependently H. Hydroxyl groups can be converted to carbamate groups byreaction with a monoisocyanate (e.g., methyl isocyanate) to form asecondary carbamate group (that is, a carbamate of the structure abovein which R is alkyl) or with cyanic acid (which may be formed in situ bythermal decomposition of urea) to form a primary This reactionpreferably occurs in the presence of a catalyst as is known in the art.A hydroxyl group can also be reacted with phosgene and then ammonia toform a primary carbamate group, or by reaction of the hydroxyl withphosgene and then a primary amine to form a compound having secondarycarbamate groups. Finally, carbamates can be prepared by atransesterification approach where hydroxyl group is reacted with analkyl carbamate (e.g., methyl carbamate, ethyl carbamate, butylcarbamate) to form a primary carbamate group-containing compound. Thisreaction is performed at elevated temperatures, preferably in thepresence of a catalyst such as an organometallic catalyst (e.g.,dibutyltin dilaurate). A hydroxyl group can be conveniently converted toa carboxylic acid by reaction with the anhydride of a dicarboxylic acid.It is possible and may be desirable to derivatize the hydroxylfunctional olefin-based block copolymer to have other functional groupsother than those mentioned, depending upon the particular coatingcomposition in which the olefin-based block copolymer is to interact.

[0035] As previously mentioned, the olefin-based block copolymer of theinvention can be used to prepare an adhesion promoter for olefinicsubstrates like TPO that provides excellent adhesion of subsequentcoating layers to the substrates. Alternatively, the olefin-basedcopolymers of the invention can be used as an additive in a curablecoating composition to provide excellent adhesion to olefinic substrateslike TPO. The adhesion promoter or coating composition of the inventionis applied directly to an unmodified and untreated plastic substrate.

[0036] First, the olefin-based block copolymer can be used in anadhesion promoter. The olefin-based block

[0037] First, the olefin-based block copolymer can be used in anadhesion promoter. The olefin-based block copolymer can be used alone asan adhesion promoter layer, particularly when it is of a sufficientlylow viscosity to flow out to form a substantially continuous layer onthe substrate. In most cases, however, it will be desirable to combinethe olefin-based block copolymer with other components, including forexample and without limitation crosslinking agents reactive with thefunctionality on the olefin-based block copolymer, solvents includingwater and organic solvents, pigments, customary coatings additives, andcombinations of these.

[0038] In one preferred embodiment, the adhesion promoter is a solutionor dispersion that includes only the olefin-based block copolymer as thevehicle. In this embodiment, it is preferred to first apply the adhesionpromoter directly to the plastic substrate and then to apply a layer ofa coating composition that includes one or more components reactive withthe olefin-based block copolymer of the adhesion promoter layer.Applying coating layers “wet-on-wet” is well known in the art.

[0039] In an alternative embodiment, the adhesion promoter includes, inaddition to the olefin-based block copolymer, at least one crosslinkingagent reactive with the block copolymer. The curing agent has, onaverage, at least about two crosslinking functional groups. Suitablecuring agents for active-hydrogen functional olefin-based copolymersinclude, without limitation, materials having active methylol ormethylalkoxy groups, such as aminoplast crosslinking agents orphenol/formaldehyde adducts, curing agents that have isocyanate groups,particularly blocked isocyanate curing agents; and combinations ofthese. Examples of preferred curing agent compounds include melamineformaldehyde resins (including monomeric or polymeric melamine resin andpartially or fully alkylated melamine resin), blocked or unblockedpolyisocyanates (e.g., TDI, MDI, isophorone diisocyanate, hexamethylenediisocyanate, and isocyanurate trimers of these, which may be blockedfor example with alcohols or oximes), urea resins (e.g., methylol ureassuch as urea formaldehyde resin, alkoxy ureas such as butylated ureaformaldehyde resin), polyanhydrides (e.g., polysuccinic anhydride),polysiloxanes (e.g., trimethoxy siloxane), and combinations of these.Unblocked polyisocyanate curing agents are usually formulated intwo-package (2K) compositions, in which the curing agent and thefilm-forming polymer (in this cased the block copolymer) are mixed onlyshortly before application and because the mixture has a relativelyshort pot life. The curing agent may be combinations of these,particularly combinations that include aminoplast crosslinking agents.Aminoplast resins such as melamine formaldehyde resins or ureaformaldehyde resins are especially preferred. For this embodiment of theadhesion promoter, the applied adhesion promoter may be either coated“wet-on-wet” with a one or more additional coating compositions, andthen all layers cured together, or the adhesion promoter layer may bepartially or fully cured before being coated with any additional coatinglayers. Curing the adhesion promoter layer before applying an additionalcoating layer may allow the subsequent coating layer to be appliedelectrostatically when the adhesion promoter is formulated with aconductive carbon black, according to methods known in the art.

[0040] Secondly, the olefin-based block copolymer can be added to avariety of coating compositions to produce coating compositions thathave excellent adhesion to plastic substrates, particularly to olefinicsubstrates including TPO. Compositions in which the olefin-based blockcopolymer may be used include primers, one-layer topcoats, basecoats,and clearcoats. The coating composition having the added block copolymerof the invention can then be applied directly to an uncoated andunmodified olefin-based substrate or other plastic to form a coatinglayer having excellent adhesion to the substrate. In the case of addingthe block copolymer to a basecoat or one-layer topcoat composition, theuse of an adhesion promoter or primer layer can be avoided. When theolefin-based block copolymer of the invention is added to a clearcoatcomposition, the clearcoat can be applied directly to a coloredpolyolefin substrate, particularly a colored TPO substrate, also knownas color-in-mold. This method produces a colored part having betterappearance, exterior durability, scratch resistance, and mar resistanceas compared to the relatively soft uncoated TPO substrate.

[0041] The compositions of the invention preferably include at leastabout 0.001% by weight of the liquid olefin-based block copolymer, basedupon the total weight of nonvolatile vehicle. In one preferredembodiment, the olefin-based block copolymer of the invention isincluded in the coating composition in an amount of from about 0.001% toabout 4% by weight of the total weight of nonvolatile vehicle. Inanother preferred embodiment, the olefin-based block copolymer of theinvention is included in the coating composition in an amount of fromabout 0.1% to about 10% by weight of the total weight of nonvolatilevehicle, more preferably from about 0.2% to about 5% by weight of thenonvolatile vehicle, and still more preferably from about 0.2% to about3% of the nonvolatile vehicle of the coating composition. Vehicle isunderstood to be the resinous and polymer components of the coatingcomposition, which includes film forming resins and polymers,crosslinkers, other reactive components such as the block copolymer ofthe invention, and other reactive or nonreactive resinous or polymericcomponents such as acrylic microgels.

[0042] The coating compositions of the invention may contain a widevariety of film-forming resins. At least one crosslinkable resin isincluded. The resin may be self-crosslinking, but typically a coatingcomposition includes one or more crosslinking agents reactive with thefunctional groups on the film-forming resin. Film-forming resins forcoating compositions typically have such functional groups as, forexample, without limitiation, hydroxyl, carboxyl, carbamate, urea,epoxide (oxirane), primary or secondary amine, amido, thiol, silane, andso on and combinations of these. The film-forming resin may be any ofthose used in coating compositions including, without limitation,acrylic polymers, vinyl polymers, polyurethanes, polyesters, polyethers,epoxies, and combinations and graft copolymers of these. Also includedare polymers in which one kind of polymer is used as a monomer informing another, such as a polyester-polyurethane or apolyether-polyurethane in which a dihydroxy functional polyester orpolyether is used as a monomer in the urethane polymerization reaction.One preferred film-forming resin is a hydroxy-functional acrylic resin.Many references describe film-forming polymers for curable coatingcompositions and so these materials do not need to be described infurther detail here.

[0043] When the coating composition includes a curing agent, orcrosslinker, the crosslinker is preferably reactive with both theolefin-based block copolymer and the polymeric film-forming resin. Thecuring agent has, on average, at least about two crosslinking functionalgroups, and is preferably one of the crosslinking materials alreadydescribed above. Aminoplast resins such as melamine formaldehyde resinsor urea formaldehyde resins are especially preferred for resinfunctional groups that are hydroxyl, carbamate, and/or urea. The coatingcompositions of the invention can be formulated as either one-component(one-package or 1K) or two- component (two-package or 2K) compositions,as is known in the art.

[0044] The adhesion promoter or coating composition used in the practiceof the invention may include a catalyst to enhance the cure reaction.For example, when aminoplast compounds, especially monomeric melamines,are used as a curing agent, a strong acid catalyst may be utilized toenhance the cure reaction. Such catalysts are well-known in the art andinclude, without limitation, p-toluenesulfonic acid, dinonylnaphthalenedisulfonic acid, dodecylbenzenesulfonic acid, phenyl acid phosphate,monobutyl maleate, butyl phosphate, and hydroxy phosphate ester. Strongacid catalysts are often blocked, e.g. with an amine. Other catalyststhat may be useful in the composition of the invention include Lewisacids, zinc salts, and tin salts.

[0045] A solvent may optionally be included in the adhesion promoter orcoating composition used in the practice of the present invention, andpreferably at least one solvent is included. In general, the solvent canbe any organic solvent and/or water. It is possible to use one or moreof a broad variety of organic solvents. The organic solvent or solventsare selected according to the usual methods and with the usualconsiderations. In a preferred embodiment of the invention, the solventis present in the coating composition in an amount of from about 0.01weight percent to about 99 weight percent, preferably for organicsolventborne compositions from about 5 weight percent to about 70 weightpercent, and more preferably for topcoat compositions from about 10weight percent to about 50 weight percent.

[0046] In another preferred embodiment, the solvent is water or amixture of water with any of the typical co-solvents employed in aqueousdispersions. When the olefin-based block copolymer is to be used in awaterborne composition, it is advantageous to include in the blockcopolymer at least one polyethylene oxide segment to aid in dispersingthe material. When modified with a polyethylene oxide segment, the blockcopolymer of the invention may be dispersed in water, optionally withother components (crosslinkers, additives, etc.) and then applied as anadhesion promoter or added to an aqueous coating composition as anaqueous dispersion of the block copolymer. Alternatively, the blockcopolymer may be blended with the film-forming polymer and thendispersed in water along with the film-forming polymer. In the lattermethod, it is contemplated that the block copolymer need not be modifiedwith a hydrophilic segment, and instead the affinity of the blockcopolymer for the film forming vehicle can be relied upon to maintainthe components in a stable dispersion.

[0047] Additional agents known in the art, for example and withoutlimitation, surfactants, fillers, pigments, stabilizers, wetting agents,rheology control agents (also known as flow control agents), dispersingagents, adhesion promoters, UV absorbers, hindered amine lightstabilizers, silicone additives and other surface active agents, etc.,and combinations of these may be incorporated into the adhesion promoteror coating composition containing the olefin-based block copolymer.

[0048] The adhesion promoter and coating compositions can be coated onthe article by any of a number of techniques well-known in the art.These include, without limitation, spray coating, dip coating, rollcoating, curtain coating, and the like. Spray coating is preferred forautomotive vehicles or other large parts.

[0049] The olefin-based block copolymer can be added to a topcoatcoating composition in amounts that do not substantially change thegloss of the topcoat. In one application, for example, the olefin-basedblock copolymer is utilized in a topcoat composition, in particular aclearcoat composition which produces a high-gloss cured coating,preferably having a 20° gloss (ASTM D523-89) or a DOI (ASTM E430-91) ofat least 80 that would be suitable for exterior automotive components.In another application, the olefin-based block copolymer may be added atopcoat composition that produces a low gloss coating, such as forcoating certain automotive trim pieces. Typical low gloss coatings havea gloss of less than about 30 at a 60° angle.

[0050] When the coating composition of the invention is used as ahigh-gloss pigmented paint coating, the pigment may include any organicor inorganic compounds or colored materials, fillers, metallic or otherinorganic flake materials such as mica or aluminum flake, and othermaterials of kind that the art normally names as pigments. Pigments areusually used in the composition in an amount of 0.2% to 200%, based onthe total solid weight of binder components (i.e., a pigment-to-binderratio of 0.02 to 2). As previously mentioned, adhesion promoterspreferably include at least one conductive carbon black in an amountthat makes the coating produced suitable for electrostatic applicationsof further coating layers.

[0051] The adhesion promoters and coating compositions can be applied atthicknesses that will produce dry film or cured film thicknesses typicalof the art, such as from about 0.01 to about 5.0 mils. Typicalthicknesses for adhesion promoter layers are from about 0.1 to about 0.5mils, preferably from about 0.2 to about 0.3 mils. Typical thicknessesfor primer layers are from about 0.5 to about 2.0 mils, preferably fromabout 0.7 to about 1.5 mils. Typical thicknesses for basecoat layers arefrom about 0.2 to about 2.0 mils, preferably from about 0.5 to about 1.5mils. Typical thicknesses for clearcoat layers or one-layer topcoats arefrom about 0.5 to about 3.0 mils, preferably from about 1.5 to about 2.5mils.

[0052] The adhesion promoters and coating compositions described hereinare preferably thermally cured. Curing temperatures will vary dependingon the particular blocking groups used in the cross-linking agents,however they generally range between 225° F. and 270° F. The curingtemperature profile must be controlled to prevent warping or deformationof the TPO substrate or other plastic substrate. The first compoundsaccording to the present invention are preferably reactive even atrelatively low cure temperatures. Thus, in a preferred embodiment, thecure temperature is preferably between 230° F. and 270° F., and morepreferably at temperatures no higher than about 250° F. The curing timewill vary depending on the particular components used, and physicalparameters such as the thickness of the layers, however, typical curingtimes range from 15 to 60 minutes, and preferably 20-35 minutes. Themost preferred curing conditions depends upon the specific coatingcomposition and substrate, and can be discovered by straightforwardtesting.

[0053] The coating compositions of the invention are particularly suitedto coating olefinic substrates, including, without limitation, TPOsubstrates, polyethylene substrates, and polypropylene substrates. Thecoating compositions may also be used, however, to coat otherthermoplastic and thermoset substrates, including, without limitation,polycarbonate, polyurethane, and flexible substrates like EPDM rubber orthermoplastic elastomers. Such substrates can be formed by any of theprocesses known in the art, for example, without limitation, injectionmolding and reaction injection molding, compression molding, extrusion,and thermoforming techniques.

[0054] The materials and processes of the invention can be used to forma wide variety of coated articles, including, without limitation,appliance parts, exterior automotive parts and trim pieces, and interiorautomotive parts and trim pieces.

[0055] The invention is further described in the following examples. Theexamples are merely illustrative and do not in any way limit the scopeof the invention as described and claimed. All parts are parts by weightunless otherwise noted.

EXAMPLE 1

[0056] To a 3-liter flask, equipped with stirrer, condenser and nitrogenblanket, were added Shell Kraton Liquid Polymer L2203 787.0 gramse-caprolactone 137.7 grams xylene 380.8 grams stannous octoate  3.2grams

[0057] The mixture was heated to and maintained at 145 degrees C for 2.5hours. After cooling, the polymer was further reduced with 291.3 gramsof xylene.

EXAMPLE 2

[0058] To a 1-liter flask, equipped with stirrer, condenser and nitrogenblanket, were added Shell Kraton Liquid Polymer L2203 187.1 g e-caprolactone 29.8 g xylene 82.4 g stannous octoate  0.7 g

[0059] The mixture was heated to and maintained at 145 degrees C for 2.5hours and cooled.

EXAMPLE 3 and Comparative Examples A and B

[0060] Coating compositions were prepared by adding the followingcomponents in order with mixing. Example 3 is a coating compositionaccording to the invention. Comparative Example A is a coatingcomposition without any adhesion additive. Comparative Example B is acoating composition containing an adhesion promoter according to theprior art. Amounts are given in grams of material. COMPAR- COMPAR- ATIVEATIVE COMPONENT EXAMPLE 3 EXAMPLE A EXAMPLE B Resimene ® 755¹ 25.0 25.025.0 Acrylic Polyol² 78.5 78.5 78.5 Acrylic Microgel³ 55.3 55.3 55.3Xylene 3 3 3 Aromatic 100 11.2 11.2 11.2 n-butyl Acetate 20.0 20.0 20.0Copolymer of 38.8⁵ — — Example 2 KRATON ® LIQUID — — 43.1 L2203⁴ Xylene11.4 — —

Results

[0061] Each of the mixtures of Example 3 and Comparative Examples A andf were poured into clear test tubes, sealed, and aged for 10 days in anupright position without turning. At the end of 10 days, each mixturewas observed to see if separate layers had formed. Comparative Example Ahad formed 2 separate layers, one layer being about 80% by volume.Comparative Example B had formed three layers, a first layer of about40% by volume, a second layer of about 35% by volume, and a third layerof about 25% by volume. Example 3 had not separated into layers andinstead remained homogeneous.

[0062] The results of the comparative testing demonstrate improvedcompatibility of the block copolymer with the organic components of arepresentative paint composition relative to unmodified olefinic dioland to the paint without the additive.

EXAMPLES 4-7 and Comparative Examples C-F Black Basecoat

[0063] A black basecoat composition was prepared having the followingcomponents: MATERIAL PARTS BY WEIGHT Resimene ® 755 11.31 Acrylic Polyol(Non-volatile portion) 28.05 Acrylic Microgel 5.88 Pigment 7.4 Solvent45.3 Additives 2.0

[0064] The black basecoat composition was used to prepare Examples 4-7and Comparative Examples C-F by mixing the following components. Partsare by weight. EXAMPLE EXAMPLE EXAMPLE EXAMPLE COMP. COMP. COMP. COMP.COMPONENT 4 5 6 7 EX. C EX. D EX. E EX. F Black Basecoat 300 300 300299.3 300 300 300 300 KRATION LIQUID 0 0 0 0 0 12.3 24.6 61.5 L2203¹Copolymer of 27.1 13.5 6.8 0.7 0 0 0 0 Example 1 n-butyl 8.0 4 2.0 5 07.5 10.8 12.0 acetate Xylene 26.9 26.0 25.5 30.0 25 34.4 38.6 44.8

Results

[0065] Each basecoat was applied directly over thermoplastic olefinsubstrate (Solvay D161B) and coated wet-on-wet with a commercialflexible 1K clearcoat. Panels were baked 30 minutes at 250° F. and aseparate set of panels were baked 30 minutes at 265° F. Adhesion of thecoating was characterized by observing the amount of paint removed bythe Tape adhesion Test for Paint Finishes (General Motors EngineeringStandard #GM9071P methods A and B. In method A the test specimen isscribed with a cross hatch and the % of paint which is removed by tapepull is recorded. In method B, a cross-cut grid pattern is scribed ontothe test specimen, and the % of paint which adheres following tape pullis recorded. OLEFIN CONTENT METHOD BASE- (G L2203 SEGMENT/ A METHOD BMETHOD A METHOD B COAT 100 G VEHICLE OF % PAINT % PAINT % PAINT % PAINTEXAM- UNMODIFIED LOSS ADHESION LOSS ADHESION PLE BASECOAT) @ 250° F. @250° F. @ 265° F. @ 265° F. 4 10 0 100 0 100 5 5.0 0 100 0 100 6 2.5 0100 0 100 7 0.25 0 100 Not Not tested tested C 0 100   0 100   0 D 5 20% 85 45   60 E 10 15%  90 10  100 F 25 0 100 0 100

[0066] These examples illustrate that the compositions of the inventionhave excellent adhesion over olefinic-based substrates, even when theinventive block copolymer is included in amounts that are two orders ofmagnitude lower than the amounts required for previously known adhesionagent compounds for coating TPO.

[0067] The invention has been described in detail with reference topreferred embodiments thereof. It should be understood, however, thatvariations and modifications can be made within the spirit and scope ofthe invention and of the following claims.

What is claimed is:
 1. An olefin-based block copolymer comprising anolefin block that is substantially saturated and at least one modifyingblock selected from the group consisting of (polyester blocks and(poly)ether blocks.
 2. An olefin-based block copolymer according toclaim 1, wherein said block copolymer has at least one functional groupselected from hydroxyl groups, carbamate groups, urea groups, carboxylicacid groups, and combinations thereof.
 3. An olefin-based blockcopolymer according to claim 1, wherein said olefin block is derivedfrom a substantially saturated polyhydroxylated polydiene polymer.
 4. Anolefin-based block copolymer according to claim 1, wherein said olefinblock is derived from a hydroxy-functional ethylene/butylene polymer. 5.An olefin-based block copolymer according to claim 1, wherein saidolefin-based block copolymer is formed by reacting a hydroxy-functionalethylene/butylene polymer that forms the olefin block with achain-extension reagent selected from the group consisting of lactones,hydroxy carboxylic acids, alkylene oxides, and combinations thereof,said chain-extension reagent forming the modifying block of the blockcopolymer.
 6. An olefin-based block copolymer according to claim 1,wherein said block copolymer has on average from about 0.7 to about 10modifying blocks.
 7. An olefin-based block copolymer according to claim1, wherein said block copolymer has on average about 1.8 to about 2modifying blocks.
 8. An olefin-based block copolymer according to claim5, wherein said dihydroxy ethylene/butylene polymer has a hydroxylequivalent weight of from about 1000 to about
 3000. 9. An olefin-basedblock copolymer according to claim 1, wherein said block copolymer has apolydispersity of about 1.2 or less.
 10. An olefin-based block copolymeraccording to claim 5, wherein said modifying block has on average fromabout 0.5 to about 25 monomer units per hydroxyl group ofhydroxy-functional ethylene/butylene polymer.
 11. An olefin-based blockcopolymer according to claim 5, wherein said modifying block has onaverage from about 2 to about 10 monomer units per hydroxyl group ofhydroxy-functional ethylene/butylene polymer.
 12. An olefin-based blockcopolymer according to claim 5, wherein said chain-extension reagentincludes epsilon-caprolactone.
 13. An olefin-based block copolymeraccording to claim 5, wherein said chain-extension reagent includesethylene oxide.
 14. An adhesion promoter comprising the olefin-basedblock copolymer according to claim
 1. 15. An adhesion promoter accordingto claim 14, further comprising an organic solvent.
 16. An adhesionpromoter according to claim 14, further including water and wherein saidolefin-based block copolymer has at least one polyethylene oxidesegment.
 17. An adhesion promoter according to claim 14, furthercomprising a crosslinker.
 18. An adhesion promoter according to claim14, wherein said block copolymer has at least one functional groupselected from hydroxyl groups, carbamate groups, urea groups, andcombinations thereof.
 19. An adhesion promoter according to claim 18,further comprising a melamine formaldehyde resin.
 20. An adhesionpromoter according to claim 14, further comprising a conductive carbonblack.
 21. A curable coating composition comprising the olefin-basedblock copolymer according to claim 1 and at least one film-formingpolymer.
 22. A curable coating composition according to claim 21,wherein said block copolymer is from about 0.001% to about 4% by weightof the total weight of nonvolatile vehicle.
 23. A curable coatingcomposition according to claim 21, wherein said block copolymer is fromabout 0.1% to about 10% by weight of the total weight of nonvolatilevehicle.
 24. A curable coating composition according to claim 21,wherein said film-forming polymer is self-crosslinking and furtherwherein said olefin-based block copolymer comprises functional groupsreactive with said film-forming polymer.
 25. A curable coatingcomposition according to claim 21, further comprising a crosslinkerreactive with said film-forming polymer and said block copolymer.
 26. Acurable coating composition according to claim 25, wherein saidfilm-forming polymer is an acrylic polymer, and further wherein each ofsaid acrylic polymer and said block copolymer has at least onefunctional group selected from hydroxyl groups, carbamate groups, ureagroups, and combinations thereof.
 27. A curable coating compositionaccording to claim 26, wherein said crosslinker is a melamineformaldehyde resin.
 28. A curable coating composition according to claim21, wherein said curable coating composition is a topcoat composition.29. A curable coating composition according to claim 21, wherein saidcurable coating composition is a basecoat composition.
 30. A curablecoating composition according to claim 21, wherein said curable coatingcomposition is a clearcoat composition.
 31. A curable coatingcomposition according to claim 21, wherein said curable coatingcomposition is a primer composition.
 32. A curable coating compositionaccording to claim 21, wherein said curable coating composition is awaterborne composition.
 33. A curable coating composition according toclaim 21, further comprising an organic solvent.
 34. A method of coatingan olefin-based substrate, comprising steps of: (a) providing anadhesion promoter according to claim 14; (b) applying the adhesionpromoter to an olefin-based substrate; (c) applying a coatingcomposition over the adhesion promoter; and (d) heating the substratehaving thereon the adhesion promoter and the coating composition to curethe coating composition.
 35. A method according to claim 34, wherein theadhesion promoter further comprises a crosslinker.
 36. A methodaccording to claim 35, further comprising a step of curing the adhesionpromoter before applying the coating composition of step (c).
 37. Amethod according to claim 34, wherein said olefin-based substrate is athermoplastic polyolefin (TPO).
 38. A method of coating an olefin-basedsubstrate, comprising steps of: (a) providing a curable coatingcomposition according to claim 21; (b) applying the curable coatingcomposition to an olefin-based substrate; and (c) heating the substratehaving thereon the curable coating composition to cure the coatingcomposition.
 39. A method according to claim 38, wherein the curablecoating composition is a primer composition.
 40. A method according toclaim 38, wherein the curable coating composition is a topcoatcomposition.
 41. A method according to claim 38, wherein the curablecoating composition is a basecoat composition.
 42. A method according toclaim 38, wherein the curable coating composition is a clearcoatcomposition and further wherein the olefin-based substrate is acolor-in-mold substrate.
 43. A method according to claim 42, wherein theolefin-based substrate is a color-in-mold thermoplastic polyolefin (TPO)substrate.
 44. An article comprising an olefin-based substratecoated-according to the method of claim
 34. 45. An article comprising anolefin-based substrate coated according to the method of claim
 38. 46.An article according to claim 45, wherein the curable coatingcomposition is a topcoat composition.
 47. An article according to claim45, wherein the curable coating composition is a basecoat composition.48. An article according to claim 45, wherein the curable coatingcomposition is a clearcoat composition and further wherein theolefin-based substrate is a color-in-mold substrate.
 49. An articleaccording to claim 45, wherein the olefin-based substrate is acolor-in-mold thermoplastic polyolefin (TPO) substrate.
 50. An articleaccording to claim 45, wherein said article is selected from the groupconsisting of appliance parts, automotive parts, and automotive trimpieces.